package com.zym.community.util;

import lombok.Setter;
import org.apache.commons.lang3.CharUtils;
import org.apache.commons.lang3.StringUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.util.HashMap;
import java.util.Map;

//敏感词过滤器
@Component
public class SensitiveFilter {

    private static final Logger logger = LoggerFactory.getLogger(SensitiveFilter.class);

    //替换符
    private static final String REPLACEMENT = "***";

    //根节点
    private TrieNode rootNode = new TrieNode();

    //初始化，在实例化bean后自动调用
    @PostConstruct
    public void init(){
        try (
                InputStream is = this.getClass().getClassLoader().getResourceAsStream("sensitive-words.txt");
                BufferedReader reader = new BufferedReader(new InputStreamReader(is));
        ){
            String keyword;
            //读取一行数据
            while ((keyword = reader.readLine()) != null){
                //添加到前缀树
                this.addKeyword(keyword);
            }
        }catch (IOException e){
            logger.error("加载敏感词文件失败。" + e.getMessage());
        }

    }

    //将一个敏感词添加到前缀树中
    private void addKeyword(String keyword){
        TrieNode tempNode = rootNode;
        for (int i = 0; i < keyword.length(); i++){
            char c = keyword.charAt(i);
            TrieNode subNode = tempNode.getSubNode(c);

            if (subNode == null){
                //初始化子节点
                subNode = new TrieNode();
                //添加到父节点之下
                tempNode.addSubNode(c, subNode);
            }

            //指向子节点，进入下一轮循环
            tempNode = subNode;

            //设置结束标识
            if (i == keyword.length() - 1){
                tempNode.setKeyWordEnd(true);
            }
        }
    }

    //过滤敏感词，返回过滤后的文本
    public String filter(String text){
        if (StringUtils.isBlank(text)){
            return null;
        }

        //指针1
        TrieNode tempNode = rootNode;
        //指针2
        int begin = 0;
        //指针3
        int position = 0;
        //结果
        StringBuilder sb = new StringBuilder();

        while (position < text.length()){
            char c = text.charAt(position);

            //跳过符号
            if (isSymbol(c)){
                //若指针1处于根节点，将此符号计入结果，让指针2走一步
                if (tempNode == rootNode){
                    sb.append(c);
                    begin++;
                }
                //无论符号在开头或中间，指针3都走一步
                position++;
                continue;
            }

            //检查下级节点
            tempNode  = tempNode.getSubNode(c);
            if (tempNode == null){
                //以begin开头的字符串不是敏感词
                sb.append(text.charAt(begin));
                //进入下一个位置
                position = ++begin;
                //重新指向根节点
                tempNode = rootNode;
            }else if (tempNode.isKeyWordEnd){
                //发现敏感词，将begin~position字符串替换掉
                sb.append(REPLACEMENT);
                //进入下一个位置
                begin = ++position;
                //重新指向根节点
                tempNode = rootNode;
            }else {
                //检查下一个字符
                position++;
            }
        }

        //将最后一批字符计入结果
        sb.append(text.substring(begin));

        return sb.toString();

    }

    //判断是否为符号
    private boolean isSymbol(Character c){
        //isAsciiAlphanumeric() 判断是否是数字或字母
        //0x2E80~0x9FFFF 是东亚文字范围
        return !CharUtils.isAsciiAlphanumeric(c) && (c < 0x2E80 || c > 0x9FFFF);
    }

    //前缀树
    @Setter
    private class TrieNode{

        //关键词结束的标识
        private boolean isKeyWordEnd = false;

        //子节点（key是下级字符，value是下级节点）
        private Map<Character, TrieNode> subNodes = new HashMap<>();

        //添加子节点
        public void addSubNode(Character c, TrieNode node){
            subNodes.put(c, node);
        }

        //获取子节点
        public TrieNode getSubNode(Character c){
            return subNodes.get(c);
        }

    }
}
